Multiple-carrier digital communications—which are also known as Orthogonal Frequency Division Multiplexing (OFDM) communications—show a great interest since the development of mobile communication, particularly with the most recent standards of: DVB-T (Digital Video Broadcasting—Terrestrial), WLAN (IEEE802.11n) (Wireless Local Area Network), Wimax (Worldwide Interoperability for Microwave Access), WiBro (Wireless Broadband), DVB-H (Digital Video Broadcasting—Handheld), T-DMB (Terrestrial Digital Multimedia Broadcasting). In a multiple-carrier digital transmission, a frequency band is divided in N multiple sub-channels, which corresponding to a sub-carrier receiving a band of frequency being equal to the bandwidth divided by the number of carriers. This results in carriers being assigned a small channel bandwidth, thus causing the communication to be sensitive to the Doppler effect which, as known in the art, is particularly present in case of a mobile receiver.
The Doppler effect is even more important in the absence of homogeneity within the different subcarriers because of the presence of multiple distinct paths for the different frequencies.
In order to compensate for Doppler effect, conventional multicarrier conventional receivers use processes and compensation devices which precisely take into account the presence of multiple and distinct communication paths for each subcarrier.
Such processing is based on the use of more or less sophisticated channel estimation and correction algorithms which are executed by means of a Digital Signal Processor (DSP) or by a specific processor integrated within the receiver and which is dedicated to such processing.
Without going through the details of different techniques known in the art for estimating and correcting channel, it suffices to recall that the estimation is generally based on the use of particular pilots or reference signals, assumed to be known from the receiver, which are periodically introduced inside the transmitted signal and which allows the estimation algorithm to evaluate, by means of successive interpolations, the characteristics of the channel for each particular subcarrier.
Generally speaking, it should be noticed that all those techniques known in the art have the drawback of requiring a non negligible processing resources from the existing DSP. Moreover, those algorithms for estimating and compensating the channel require calculations performed on a large set of data, thus requiring the use of a large amount of memory with the DSP processor.
It can thus be seen that the channel estimate algorithms implement complex and expensive electronic microcircuits.
Additionally, it is important to underline that these estimate techniques operate satisfactorily as long as the Doppler effect is limited in a low value, in the order of 10% of the inter-carrier space allocated to the sub-carrier, that means in practice that one hundred Hz correspond to an inter-carrier space in the order of 1 kHz.
Such limits are reached when the mobile receiver is moved at an increasing speed, in the order of one hundred kilometers per hour, what tends to be commonplace in the context of a contemporary mobile communication.
In order to take into account such particular situation wherein the mobile receiver is moved at a significant speed, the channel estimation and correction techniques which were mentioned above are to be combined with supplementary techniques in order to further take into account the increasing value of the Doppler effect and thus permit to cancel the interference between the carriers. Such techniques are conventionally designated under the name of Inter Carrier Interference (ICI) Cancellation or simply ICI Cancellation.
Clearly, the implementation of these supplementary techniques complicates the digital multi-carrier receiver architecture.